Generally, in CVD reactors, the material being deposited not only deposits on the wafer, as is desired, but some material, not necessarily the same as that on the wafer, is also deposited on the reactor chamber walls and other parts within the reactor, notably the wafer support and a ring positioned around the wafer support in many reactors. Periodically, in order to maintain a repeatable process, the chamber has to be cleaned. Such chamber cleaning typically occurs by heating the wafer support, chamber walls and other parts to a suitably high temperature and admitting a flow of a halogen containing gas, for example Hcl.
Reactors for epitaxial deposition commonly employ a susceptor and a surrounding ring which helps to control the temperature of the susceptor. These components are usually made from graphite and coated with silicon carbide (SiC). Eventually, the Hcl etch will penetrate the SiC coating which will cause rapid deterioration of the properties of the deposited films. Hence, they must be replaced. One type of well-known reactor employs thermocouples adjacent the ring for sensing the temperature of the rings surrounding the susceptor, which in turn is an indirect measure of the temperature of the susceptor and a wafer positioned on it. These thermocouples are usually sheathed with quartz. Frequent thermal cycling of the quartz to temperatures in excess of 1000.degree. C. causes devitrification of the quartz sheath and failure of the thermocouples, thus requiring replacement.
Commonly, the chamber is formed of quartz. A problem in high temperature chemical vapor deposition operations is that reactant gases may coat the interior of quartz chamber walls. Coatings on the chamber walls can have a number of undesirable aspects including the flaking of particles off the walls and the need for more frequent cleaning of the chamber. Some of the material depositing on the quartz chamber walls may not be etched away when the chamber is cleaned. If sufficient deposits gather, the quartz chamber locally loses its transparency and will heat rapidly by radiation from the lamps conventionally positioned adjacent the exterior of an upper chamber wall and adjacent the exterior of a lower chamber wall. This eventually requires the need to wet clean or even to replace the quartz chamber.
If the chamber walls become too hot, the reactant gases can deposit on the walls in similar fashion to depositing on a wafer. Quartz is the material of choice for chamber walls because quartz is to a large extent transparent to the heat energy provided by the lamps. As the wafer, the susceptor and the surrounding compensation ring are heated by this radiant energy, they reradiate energy back towards the chamber walls. Some of this reradiated energy has a wave length at which a significant portion of the energy is absorbed by the quartz chamber walls. Consequently, to maintain the temperature of the walls below that at which deposition on the walls will occur, it is customary to flow air or other coolant across the lamps and adjacent chamber walls. This cooling, however, can cause some sections of the chamber walls to be maintained at temperatures at which reactant gases can condense on those cooler areas. Other chamber components, such as a spider used to support the susceptor and a stand used to support the ring, are also commonly made of quartz and are therefore subject to the same problems of devitrification and exposure to processing gases.
The need to replace susceptors, rings, thermocouples, chambers and various other chamber components naturally results in down-time for the reactor and significant costs for replacement components. In addition, there is significant time and expense in returning the reactor to the condition to provide the desired film properties on the wafers being coated.
It is an object of this invention to significantly extend the life of the components within the CVD chamber. It is a further object of this invention to decrease the amount of deposits on the chamber walls and some components in the CVD chamber to extend their life. It is also an object to increase the cleaning efficiency of the cleaning agent. Related to the last two objects, it is a further object of this invention to reduce down time and hence increase throughput.